During the previous Grant Period (NIH 1RO1 EY 00965) we established that not only adenosine but also uridine, in the presence of glutamine, is capable of stimulating the rabbit corneal endothelial pump, albeit in the same high concentration - 5mM. During the last month of the previous (extended Grant) Period, we found that GABA (gamma amino butyric acid), in the absence of any other organic compound, at the extremely low concentration range 1-10 micromolar, is at least as good as any previous adenosine or adenosine-glutathione combination (see enclosed article No. 2). We established the presence of GABA receptor in the endothelium, using accepted agonists and antagonists. This is the first instance of GABA regulation of any fluid pump and the first instance of GABA effect outside the central nervous or invertebrate neuromuscular junction systems. We wish first to chracterize it well pharmacologically, using our (now standard) method of perfusion. We also wish to analyze the stroma and the aqueous humor the their GABA content and/or materials with GABA-like activity. GABA (like adenosine) does not increase corneal survival in the standard temperature reversal conditions over 7 hours. Since the problem of stimulating the extent of pumping seems to be solved by using GABA, we wish to try different hormones, amino-acids etc., in presence of GABA, to see whether we can improve the survival time as well.